Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
The 3rd Generation Partnership Project (3GPP) is a globally applicable third generation mobile phone system specification that is a result of collaboration between various groups of telecommunications associations, including the European Telecommunications Standards Institute, the Association of Radio Industries and Businesses/Telecommunication Technology Committee (ARIB/TTC), China Communications Standards Association, and the Alliance for Telecommunications Industry Solutions. 3GPP work is ongoing with Universal Terrestrial Radio Access Network (UTRAN) long term evolution (LTE). The 3GPP RAN2 working group has defined a Discontinuous Reception (DRX) mechanism to save battery life and resources of user equipment (UE). The main principle in DRX is that the user equipment (UE) behavior is defined relative to the successful decoding of the Physical Downlink Control Channel (PDCCH) by the UE. When the UE is in DRX, the UE is allowed to stop monitoring the PDCCH temporarily. DRX uses one or two pre-defined cycles (long and/or short cycles), at the beginning of which the UE monitors the PDCCH over a certain amount of transmission time intervals (TTIs), according to an “On Duration” Timer. The PDCCH carries downlink (DL) assignments as well as uplink (UL) grants.
Whether the UE is awake (e.g., is monitoring the PDCCH) or asleep after the On Duration period, depends on activity (i.e., possible reception of PDCCH control data during the period). To avoid unnecessary scheduling and to avoid wasting of radio resources, the base station (e.g., eNodeB) should know the state of the UE when transmitting downlink data from the base station to the UE. Thus, a set of clear rules for changing from the active state to DRX and back are defined in Reference [1] (3GPP Technical Specification (TS) 36.321, “Medium Access Control (MAC) Specification,” V10.1.0, March, 2011).
FIG. 1 illustrates a traditional DRX mechanism which includes a long DRX cycle and a short DRX cycle. The UE turns on its receivers to monitor scheduling information on PDCCH. If no transmission on the PDCCH is detected, i.e., the UE wakes but no transmission on the PDCCH is detected, the UE may turn off its receivers, i.e., go to sleep, to reduce battery consumption. After a sleep period, the UE again turns on its receivers to monitor the PDCCH. The cycle is called a Long DRX cycle. If a transmission on the PDCCH is detected at a time, i.e., the UE wakes and a transmission on the PDCCH is detected, the UE shall continuously monitor the PDCCH, i.e., an Inactivity Timer is started to extend the active time for monitoring the PDCCH. When the Inactivity Timer expires, a short DRX cycle is started, during which the UE wakes with a shorter sleep period than that sleep period used in the long DRX cycle. After the short DRX cycle, the UE enters the long DRX cycle. The DRX mode is important to increase the standby times of mobile devices such as small handsets.
Reference [1] also provides some other parameters, such as drx-Retransmission Timer, mac-Contention Resolution Timer, HARQ RTT Timer and others that used in the DRX mode. FIG. 1 does not show these parameters for simplicity.
Currently, the CoMP Work Item was approved in 3GPP RAN plenary #53 meeting. A UE in a CoMP scenario means that the UE is served by at least two Base Stations (BSs) at the same time. In the CoMP scenario, the at least two Base Stations (BSs) transmit scheduling information on separate (e)PDCCHs, and the UE shall monitor the separate (e)PDCCHs at the same time. The enhanced PDCCH (ePDCCH) is used to supplement, augment, or replace the PDCCH control channel. When two or more (e)PDCCHs are used, the (e)PDCCHs are allocated with different resource locations to avoid interference. For example, a conventional physical downlink control channel (PDCCH) is transmitted in a first region of a physical downlink control channel structure while an enhanced physical downlink control channel (ePDCCH) is transmitted in a second region of the physical downlink control channel.
There is a need for a new DRX method in the CoMP scenario.